In the prior door opening mechanism of U.S. Pat. No. 4,126,162 there is a hydraulic door actuator with a mechanical means for locking the same in its position when the door is closed and another means for simultaneously directing hydraulic fluid to one side of the door actuator piston for also holding the door actuator in its door closed position. A manually operated means is operable for simultaneously unlocking the door actuator from its door closed position and for opening a valve to direct pressure fluid to the other side of the piston to move the piston toward door opening position. It has been found that it is unnecessary to retain fluid pressure in the door actuator for holding it in door closing position when the mechanical means is locking the actuator in its door closed position. Also, it is undesirable in any hydraulic system to unnecessarily subject any portion thereto to high fluid pressure.
In another prior art refueling door opening device a manually operated rotary cam shaft when rotated to one position opens a first valve to connect a pressure source to a first conduit that is connected to one side of a door opening actuator and opens a second valve to connect a reservoir to a second conduit connected to the other side of the actuator. When rotated to another position the cam shaft opens a third valve to connect the pressure source to the second conduit and opens a fourth valve to connect the reservoir to the first conduit.